Method and apparatus for vapor coating



Jan 5, 1954 P. GODLEY, 2ND x-rrAx. 2,665,226

METHOD AND APPARATUS FOR VAFOR COATING Filed April 2'?, 1950 2 Sheets-Sheet 1 ATTORNEYA Jam 5, 1954 P. GODLEY, zNn rs1-AL 2,665,226

METHOD AND APPARATUS FOR VAPOR COATING Filed April 2'?, 1950 2 Sheets-Sheet 2 VENTORS ATTORNEY Patented Jan. 5, 1954 METHOD AND APPARATUS FOR VAPOR GOATING Philip Godley 2nd, Lexington, Philip J. Clough, Reading, andRObert A. Stanffer, Weston, Mass., assignorsrv to National Research Corporatioxi,A Cambridge, Masas., a corporation of Massachusetts Application April'27, 1950, Serial No. 158,494

7- Claims. (Cl. 117-107) This invention relates -Ato `coating and mure particularly to vacuum deposition coating of the type wherein a metal, such as aluminum, is vapor-ized 'in avacuum and the vapors thereof are condensedon, asubstrate which is moved past desirable to have a relatively small evaporating area heated toa high temperature so as to decrease the amount'of radiant heat which is transferred vto the substrate per gram of aluminum coated on. the substrate.

In the Copending application of Godley, filed oneven date herewith, one improved processVY and apparatus is described for accomplishing the above objectives.

,It is a -prniralobiect Qf the present invention to provide vapor-deposition processes of the above type whichare simple and cheap to operate, and'which have a high coating efficiency with a minimum of outgassing of the substrate to b e coated,

Another object ofthe present invention is to provide an improved process for obtaining a uniform distribution ofl coating vapors forooating wide sheets of substrateathigh rates of speed with accurate control of coating thickness.

Still another vobject- Vof the present invention is, to provide'an-improved apparatus for accomplishing the aboveV processes.

"Other objects of the invention will in part be obvious and will part appear hereinafter.

The invention accordingly comprises the apparatus Vpossessing the construction, combination of elements and arrangement of parts, and the process involving theseveral steps and the relation and the orderlof one'or more ofsuchsteps with Vrespect to -each of the others .which are exemplified inthe yfollowing detailed disclosure,

and the scope oftheapplication ofwhich will be indicated in the claims.

.For a fuller understanding f the nature and objects of the inventiom reference should' behad to thev following .detailed descrptiontaken in ,corlntiorik with the accompanying drawings wherein:

Fig. Y 1 is a. diagrammatic.. schematic. partially sectionalrview of one embodiment of the invention Fia 2- is` .a diagrammatic., schematic, `.fresmentary View affanculo 9f..1 *?i,g..,1. teken @19mg Fig. 3 is a diagrammatic, schematic, fragmentary viewv ofy a modification of theFigs. 1'an`d '2 embodiment of the invention;

Fig. vlis a diagrammatic, schematic View of another embodiment of the invention;

" Fig. 5 is a diagrammatic, schematic( view of still another embodiment of the invention;

Eig. 6 is a diagrammatic, schematic view of still another embodiment of the invention; and Fig. '7 is a diagrammatic, schematic viewof a modified arrangement of substrate guidingr means.r

In' the practice ofthe present invention, there is provided a usual' vacuum coating v'chamber which can be evacuated to pressuresv in the micron range. Associated with this chamber there is provided a low-temperature zone for confining themetal to be coated, this low-temperaturezone being preferably arranged t0 maintain the metal in a, moltenY pool at a temprature somewhat above its melting' point.'

In a preferred form of the processv of this invention, the metal comprises aluminum, and for simplicity of description aluminum will be referred'to hereinafter. The large body offaluminum confined in the low-temperature zone is preferably held in a' container which is substantially inert to molten' aluminum at' relatively low temperatures on the order of 800 C. There is also provided a high-temperature evaporavtion z'one` where the aluminum may be heated to a high temperature', preferably above 1300 C. For feeding'the molten aluminum from thelowtemperature zone to the evaporation zone, there is"included a wick element which extends into the poolof molten aluminum and is wet byfthe molten aluminum. The aluminum, which wets the wick element, travels from' the low-temperature zone to thehigh-.temperature zone where it is rapidly evaporated. This wick element preferablycomprises Va material which is,A relatively inert toaluminum Vat hightemperatures, and preferably comprises anitride or a carbide.

The wick element alsopreferably actsas a support for the aluminum in the high-temperature evaporationzone.

In the present invention the wick element preferably has a high resistance vwith respect to the valuminum to bey coated, andthe wick element is heated to the desiredhigh evaporation temperaturev by passing an electric currentin series through the wickelement Aand the aluminum in thepool into whichthe' wick element extends. Due tothe high resistancel of the wick element. the' Wick" .element isf heated itQ the desired' hslh th' inveuuou, the aluminum in the container" 42 is heated, such 'as by an induction @ou (not shown), so as to melt the aluminum therein. A pressure in excess ci the pressure within the vacuum chamber l2 is then created on the surfaee or the aluminum in container 42, this pressure being preferably created by permitting the entrance of an inert gas through the tube 48. This pressure forces the molten aluminum up the tube' ed, the' aluminum lling the enlarged portion 6 and contacting the ends of the two wick elements 3B. Current is then passed through the aluminum and the two wickelements to heat the wick elements 32 to the desired high temperature. The aluminum thenwets the two wick elements, as at 25a, and is evaporated as it climbs up the two wick elements'.

In the Fig. l embodiment of the invention, a'

single U-'shaped wick element 5i! is employed and the aluminum is held in contact therewith by means o two liquid-feeding devices 52 and 5d which, in a preferred form of the invention, comprise liquid-feeding barometric legs of the type discussed in connection with Fig. 3. The two barcmetric legs `52 and 54 are preferably in series, in an electrical circuit, with the battery 56 and with the wick element 59. Appropriate leads 58 are included for competing the electrical circuit. In this embodiment of the invention, all o1" the electrical connections to the aluminum may be outside of the vacuum housing I dening the vacuum chamber, so that no electrical connections need be made to the interior of the vacuum chamber. n

In the Fig. 5 embodiment of the invention, there are provided two -barometric legs 52 and all for feeding molten aluminum to two wick elements 5e held by a pair of wick holders 52. In this form of the invention both of the wicks 8D preferably extend across the whole width of the substrate and are preferably positioned in two planes which are parallel and slightly spaced apart. This arrangement has the advantage that coating can continue across the entire substrate even if one of the wick elements should break, it being apparent, however, that if one of the wick elements should break the coating speed will be cut in half.

In the Fig. 6 form of the invention, one barometric leg l?. is provided and two wick elements lil, held by two wick holders 74, are fed by the single baro-metric leg. In this embodiment of the invention each wick element 10 has a curved upper portion 'll in Contact with the aluminum, the main portion of the wick element extending downwardly from the level of the aluminum at the top of the barometric leg 12. By this arrangement -the wetting of the wick element 10 by the aluminum is assisted by gravity. Since this wetting may be sufficiently rapid to take place at a rate greater than the rate of evaporation, means are provided at 80 for collecting the excess molten aluminum which runs down the wick element 7i?. Additionally, if desired, aluminum may `be fed upwardly in the barometric leg l2 at a rate faster than the evaporation rate so as to assure complete coverage of the wick elements at all times by the molten aluminum.

In the operation of the embodiments shown in Figs. i through 6, the same procedures are employed as those discussed previously. In these embodiments of the invention the barometric legs and the source of aluminum may be wholly within the vacuum chamber l2, or may extend through the housing `Il) dening the vacuum lll gaat f' a usages-u ai a at atea* tiori, 1the alumir'iurriin the ,large 'source and' iii the barometric legs is preferably maintained at a temperature not muchin excess Vf the melting point so as to obviate the necessity for special inert coatings. y i Y As' described more fullyl ifi the cpe'iding application of Stauier, led on even date herewith, it is 4citen advantageous particularly in the case of extremely heat-sensitive materials', to com bine a plurality of separate coating operations with cooling of the substrate between these various operations. This cooling kserves to remove from the substrate heat carried theretoby the vapors. The Fig. 7 embodiment of the invention is particularly 'adapted for practicing this' cooling of the substrate inv conjunction lwith the' coating processes of the present invention. In Fig. 'Y the source or aluminum vapors is illustrated as a wick elementr 88, which may be arrange-d in the manner shown, for example, in Fig. 4. The substrate I6, in moving past the 'wick element 38, travels in a number of convolutions so that it is moved successively into and out of the vapor stream emanating from the wick element 38. This is achieved by providing a. plu-- rality cf rolls 92 through |04. In one lpreferred form of this aspect of the invention, these rolls e2 through |64 are cooled, such 'as by circulating f cold water therethrough so that the substrate in.

contact with these rolls is ceoled lwhile passing is passing over rolls 92, 96,v l0() and |04; vDuring the passage over the other rolls, the substrate is only being cooled. y

rIhe expression group IVa and group Va'r metals is intended to include those metals in groups IVcL 'and Va onV the Periodic Chart of the Atoms, Henry D. Hubbard, 1947 edition, W. M. Welch Manufacturing Company. These metals are titanium, zirconium, hafnium, vanadium. columbium and tantalurn.

Since certain changes may be made in the above process and apparatus Without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description, or shown in the accompanying drawings, shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

1. Apparatus for coating a substrate with aluminum by vacuum-evaporation of said aluminum and condensation of said aluminum on said substrate, said apparatus comprising means dening a vacuum-tight chamber, means for conrlning said aluminum within said chamber, a reservoir for holding a pool of molten aluminum in said chamber, means comprising a wick element, said Wick element having a high resistivity as compared to said aluminum, said wick element being substantially inert to molten aluminum and having at least a surface stratum comprising a compound selected from the class consisting of the nitrides and carbides of the metals titanium, zirconium, hafnium, vanadium, columbium and tantalum, means for heating said wick element to a temperature higher than the temperature of said molten aluminum, one end of said wick element being immersed in said molten pool of aluminum so that said wick element is Wet by said aluminum and said aluminum is evaporated from said wick element by said high temperature, said wick element extending upwardly from the surface of the molten pool so as to radiate aluminum vapors towards the substrate to be coated, said means for heating said wick element comprising an electric circuit including said pool of aluminum and said wick element arranged in series, and means for moving said substrate past said wick element to give a substantially uniform coat of said aluminum on said substrate.

2. The apparatus of claim 1 wherein means are included for feeding aluminum to said pool to maintain said pool at a predetermined level to assure wetting of said wick by molten aluminum during coating.

3. The apparatus of claim 1 wherein said means for moving said substrate comprises means for guiding said substrate past said wick element in a plurality of convolutions so that said substrate is moved, a number of times, into and out of the vapor stream generated by aluminum evaporating from said wick element.

4. The apparatus of claim 1 wherein said wick element comprises a rod and said substrate moving means is arranged to move said substrate past said Wick element so that the transverse dimension of said substrate remains, during coating, substantially parallel to the long dimension of said rod.

5. The apparatus of claim 1 wherein two wick elements are positioned in said vacuum-tight chamber, said two wick elements being positioned in substantially the same plane, and said substrate moving means is arranged to move said substrate in a plane substantially parallel to, and spaced from, the plane of said wick elements.

6. A process for coating a substrate with aluminum by vacuum-evaporating said aluminum and condensing said aluminum on said substrate. said process comprising the steps oi providing a source of said aluminum in a vacuum chamber.

evacuating said chamber, melting at least a por-I tion of said aluminum in said source of aluminum. providing a wick element which is wettable by said aluminum, said Wick element being substantially inert to molten aluminum and having at least a surface stratum comprising a compound selected from the class consisting of the nitrides and carbides of the metals titanium, zirconium, hafnium, vanadium, columbium and tantalum. conning said molten aluminum in a pool in contact with said Wick element, heating said wick element to a temperature higher than the temperature in said pool by passing an electric current in series through said Wick element and said aluminum in said pool, said wick element having a high resistivity as compared to said aluminum, evaporating, by said high temperature, that aluminum which Wets said Wick element. and moving said substrate past said wick element to coat aluminum on said substrate.

7. The process of claim 6 wherein said wick element comprises a surface stratum of a compound selected from the class consisting of the carbides of titanium, zirconium, hafnium, vanadium, columbium and tanta-lum.

PHILIP GODLEY 2ND. PHILIP J, CLOUGI-I. ROBERT A. STAUFFER.

References Cited in the le of this patent UNITED STATES PATENTS Number Name Date 2,159,297 Shover May 23, 1939 2,351,536 Osterberg et al June 13, 1944 2,363,781 Ferguson Nov. 28, 1944 2,382,432 McManus et al. Aug. 14, 1945 2,387,970 Alexander Oct. 30, 1945 2,450,856 Colbert et al. Dec. 31, 1946 

6. A PROCESS FOR COATING A SUBSTRATE WITH ALUMINUM BY VACUUM-EVAPORATING SAID ALUMINUM AND CONDENSING SAID ALUMINUM ON SAID SUBSTRATE, SAID PROCESS COMPRISING THE STEPS OF PROVIDING A SOURCE OF SAID ALUMINUM IN A VACUUM CHAMBER, EVACUATING SAID CHAMBER, MELTING AT LEAST A PORTION OF SAID ALUMINUM IN SAID SURCE OF ALUMINUM, PROVIDING A WICK ELEMENT WHICH IS WETTABLE BY SAID ALUMINUM, SAID WICK ELEMENT BEING SUBSTANTIALLY INERT TO MOLTEN ALUMINUM AND HAVING AT LEAST A SURFACE STRATUM COMPRISING A COMPOUND SELECTED FROM THE CLASS CONSISTING OF THE NITRIDES AND CARBIDES OF THE METALS TITANIUM, ZIRCONIUM, HAFNIUM, VANADIUM, COLUMBIUM AND TANTALUM, CONFINING SAID MOLTEN ALUMINUM IN A POOL IN CONTACT WITH SAID WICK ELEMENT, HEATING SAID WICK ELEMENT TO A TEMPERATURE HIGHER THAN THE TEMPERATURE IN SAID POOL BY PASSING AN ELECTRIC CURRENT IN SERIES THROUGH SAID WICK ELEMENT AND SAID ALUMINUM IN SAID POOL, SAID WICK ELEMENT HAVIING A HIGH RESISTIVITY AS COMPARED TO SAID ALUMINUM, EVAPORATING, BY SAID HIGH TEMPERATURE, THAT ALUMINUM WHICH WETS SAID WICK ELEMENT, AND MOVING SAID SUBSTRATE PAST SAID WICK ELEMENT TO COAT ALUMINUM ON SAID SUBSTRATE. 